With the advances in electronic technology in recent years, the control of amplifier units (which selectively extract a number of input signals via a function switch) and tape deck units (which record or play back audio or video cassette tapes) is performed by microcomputers. Recently, for instance, the amplifier unit and the tape deck unit each have a microcomputer which recognizes the operating mode of the microcomputer in the other unit by mutual exchange of control data. One benefit of each unit having its own microcomputer is the increased processing speed that can be achieved.
FIG. 1 shows an example of a prior art input/output switching circuit in which a microcomputer is provided in each of an amplifier unit and a tape deck unit.
The amplifier unit 10 includes an amplifier control microcomputer 12 (referred to as "first microcomputer" hereafter) for selectively switching the input signals at jacks 14a through 14d. The first microcomputer 12 of the amplifier unit 10 detects and determines the current mode of tape deck unit 16 through keyswitches 12a through 12c. Tape deck unit modes include record and playback.
The tape deck unit 16 passes control signals to first microcomputer 12, through a communication line 18 connected between jacks 14e and 14f for selecting signals output through a speaker 20 via an input selector switch 22 (referred to as "input selector" hereafter). Additionally, first microcomputer 12 transmits the switching mode of the input selector 22 to tape deck unit 16 through communication line 18.
The tape deck unit 16 is provided with a tape deck control microcomputer 24 (referred to as "second microcomputer" hereafter) for controlling a tape drive mechanism (not shown) which drives a cassette tape and for executing the signal selection of a record/playback head 26. The second microcomputer 24 controls the cassette mechanism according to the mode of keyswitches 24a through 24e, and executes the selection of either recording signals to a record/playback head 26 or the playback of recorded signals. Moreover, the second microcomputer 24 detects and determines the mode of amplifier unit 10 according to control data output from the first microcomputer 12 through communication line 18.
When tape deck unit 16 is selected at the amplifier unit 10, first microcomputer 12 automatically passes the appropriate control data to the second microcomputer 24 to place tape deck unit 16 into playback mode. When another input is selected at the amplifier unit 10 microcomputers 12 and 24 automatically place tape deck unit 16 into a stop mode. Additionally, the second microcomputer 24 transmits control data to amplifier unit 10 through the communication line 18 indicating the mode of the cassette mechanism (playback, fast forward, rewind, stop, record) in tape deck unit 16.
When the input keyswitch 12a of first microcomputer 12 is closed, first microcomputer 12 closes a first switch 22a and opens second and third switches 22b and 22c of input selector 22. Since first switch 22a is closed, input audio/video signals from jack 14a are transmitted to a buffer 28. These audio/video signals are input to a pre-amplifier 30 from buffer 28 and subsequently output from speaker 20 via a volume controller 32 and a power amplifier 34. The output of the buffer 28 is also transmitted to tape deck unit 16 through a buffer amplifier 36 as an input signals.
The output of buffer amplifier 36 is supplied through jack 14d and input to jack 14g on tape deck unit 16 through a first connection cable 38a. The signal input to jack 14g is amplified by a recording amplifier 40 and, if tape deck unit 16 is in the recording mode, is added to a bias signal from a bias oscillator 42 and then applied as a recording signal to the record/playback head 26 via a first head circuit switch 44a which is closed. At this time, first microcomputer 12 transmits data indicating the closed state of first switch 22a and the open states of the open states of the second and third switches, 22b and 22c, to the second microcomputer 24 of tape deck unit 16 through the communication line 18.
When the keyswitch 12c of amplifier unit 10 is closed, first microcomputer 12 closes the third switch 22c of input selector 22 and opens the first and second switches, 22a and 22b. If tape deck unit 16 is in the playback mode, played-back signals from the tape are input from a jack 14h on tape deck unit 16 to jack 14c on the amplifier unit 10 through a second connection cable 38b and are passed through third switch 22c to the speaker 20. Also, first microcomputer 12 transmits data indicating the closed state of third switch 22c and the open states of first and second switches, 22a and 22b, to the second microcomputer 24.
Thus, if tape deck unit 16 is in playback mode, second microcomputer 24 places the cassette mechanism into playback mode according to data from first microcomputer 12 and inputs the played-back signals obtained from the record/playback head 26 via a second head circuit switch 44b which is closed and a playback amplifier 46 to the jack 14c. It is thus possible to play back the signals through the speaker 20.
Accordingly, during recording, signals are passed from amplifier unit 10 to tape deck unit 16 through first connection cable 38a connected between the jacks 14d and 14g, while second connection cable 38b connected between jacks 14c and 14h is not used. Conversely, during playback, signals are passed from tape deck unit 16 to amplifier unit 10 through second connection cable 38b connected between jacks 14h and 14c, while first connection cable 38a connected between jacks 14d and 14g is not used. As a result, during any operation of the prior art device shown in FIG. 1 either one of the connection cables 38a and 38b connected between amplifier unit 10 and tape deck unit 16 are not used and is, thus, wasted.
Although the above exemplary description is directed to analog audio signals, the same applies for digital audio signals from a digital audio tape recorder or to video signals from a VTR.
The prior art input/output switching circuit described above cannot operate correctly unless the respective signal lines are connected to recording amplifier 40 of tape deck unit 16 for signals from the amplifier unit 10, and to input selector 22 of amplifier unit 10 for playback signals from tape deck unit 16. In this way, a pair of connection cables for the recording input signal and the playback output signal are required between tape deck unit 16 and amplifier unit 10. Therefore, when the number of amplifier units and tape deck units is increased, the number of connection cables, large as it already is, will increase further.